Ink jetting devices are well known in the art. As described in U.S. Pat. No. 6,547,380, ink jet printing systems are generally of two types: continuous stream and drop-on-demand. In continuous stream ink jet systems, ink is emitted in a continuous stream under pressure through at least one orifice or nozzle. The stream is perturbed, causing it to break up into droplets at a fixed distance from the orifice. At the break-up point, the droplets are charged in accordance with digital data signals and passed through an electrostatic field that adjusts the trajectory of each droplet in order to direct it to a gutter for recirculation or a specific location on a recording medium. In drop-on-demand systems, a droplet is expelled from an orifice directly to a position on a recording medium in accordance with digital data signals. A droplet is not formed or expelled unless it is to be placed on the recording medium. There are generally three types of drop-on-demand ink jet systems. One type of drop-on-demand system is a piezoelectric device that has as its major components an ink filled channel or passageway having a nozzle on one end and a piezoelectric transducer near the other end to produce pressure pulses. Another type of drop-on-demand system is known as acoustic ink printing. As is known, an acoustic beam exerts a radiation pressure against objects upon which it impinges. Thus, when an acoustic beam impinges on a free surface (i.e., liquid/air interface) of a pool of liquid from beneath, the radiation pressure which it exerts against the surface of the pool may reach a sufficiently high level to release individual droplets of liquid from the pool, despite the restraining force of surface tension. Focusing the beam on or near the surface of the pool intensifies the radiation pressure it exerts for a given amount of input power. Still another type of drop-on-demand system is known as thermal ink jet, or bubble jet, and produces high velocity droplets. The major components of this type of drop-on-demand system are an ink filled channel having a nozzle on one end and a heat generating resistor near the nozzle. Printing signals representing digital information originate an electric current pulse in a resistive layer within each ink passageway near the orifice or nozzle, causing the ink vehicle (usually water) in the immediate vicinity to vaporize almost instantaneously and create a bubble. The ink at the orifice is forced out as a propelled droplet as the bubble expands.
Ink jet printing processes may employ inks that are solid at room temperature and liquid at elevated temperatures. Such inks may be referred to as hot melt inks or phase change inks. For example, U.S. Pat. No. 4,490,731 discloses an apparatus for dispensing solid ink for printing on a substrate such as paper. In thermal ink jet printing processes employing hot melt inks, the solid ink is melted by the heater in the printing apparatus and utilized (i.e., jetted) as a liquid in a manner similar to that of conventional thermal ink jet printing. Upon contact with the printing substrate, the molten ink solidifies rapidly, enabling the colorant to substantially remain on the surface of the substrate instead of being carried into the substrate (for example, paper) by capillary action, thereby enabling higher print density than is generally obtained with liquid inks. Advantages of a phase change ink in ink jet printing are thus elimination of potential spillage of the ink during handling, a wide range of print density and quality, minimal paper cockle or distortion, and enablement of indefinite periods of nonprinting without the danger of nozzle clogging, even without capping the nozzles.
Pigmented phase change ink compositions that include various dispersants are known. For example, pigmented phase change ink compositions are disclosed in U.S. Patent Publication No. 2003/0127021 and U.S. Pat. Nos. 5,053,079, 5,221,335, and 6,001,901.
Microfluidics is an area of microfabrication that focuses on the manipulation of liquids and gases in channels with cross-sectional dimensions ranging from a few nanometers to hundreds of micrometers. Microfluidics is a rapidly growing technology impacting a number of research areas including chemical sciences, biomedical research, and drug discovery. Applications include but are not limited to genomics, proteomics, pharmaceutical research, processing of nucleic acids, forensic analysis, cellular analysis, and environmental monitoring, among others.
One of the primary focuses of microfluidic technology is directed toward making increasingly complex systems of channels with greater sophistication and fluid-handling capabilities.
Some of the first microfluidic devices were fabricated using conventional techniques that originated from the microelectronics and integrated circuit industry. Such devices were typically made in glass, silicon or quartz. Processes that were originally designed for microelectronics, such as standard photolithographic methods, were then applied to glass or silicon substrates in order to build two-dimensional channel networks for sample transport, separation, mixing and detection systems on a monolithic chip. For example, to illustrate an example of an earlier process for microfluidic device fabrication based on silicon and glass substrates, a mask is prepared having both transparent and opaque regions that are patterned as a negative image of the desired channel design. A UV-light source transfers a design from the mask to a photoresist (analogous to photographic film) that was previously deposited on the substrate using traditional spin-coating methods. The photoresist is then developed in a solvent that selectively removes either the exposed or the unexposed regions. The open areas are then chemically etched into the substrate, whereby the etching time, etching conditions and crystalline orientation of the substrate control the depth of the channels and the shape of the sidewalls, respectively. Finally, the photoresist is removed and the channel system is closed by thermally bonding the patterned substrate to a cover plate. More complex, three-dimensional systems can then be built by bonding several of these patterned layers together.
Although the above described microfluidic device fabrication and layering process based on glass and silicon substrates has some benefits, it also embodies several limitations that include, but are not limited to: (1) material limitations related to the use of glass substrates; (2) material costs; (3) the many processing steps involved; (4) limitations in geometrical design due to the isotropicity of the etching process; and (5) surface chemistry limitations with respect to silicon substrates. Furthermore, typical microfluidic devices require cleanroom facility and expensive MEMS/semiconductor microfabrication equipment to build.
Microarrays is another area of microfabrication that focuses on the preparation of a substrate with patterned or random reaction sites. Complex lithography techniques are also generally used for forming such microarrays. The microarrays are important, for example, in such areas as biomedical research, drug discovery, sample analysis, sensor design, and the like.
Thus, there is a need for a method of fabricating microfluidic devices and microarrays that overcomes these limitations and, in particular, eliminates the need of expensive microlithography equipment to perform the processing, and is relatively inexpensive.
The disclosures of each of the foregoing patents and publications are hereby incorporated by reference herein in their entireties. The appropriate components and process aspects of the each of the foregoing patents and publications may also be selected for the present compositions and processes in embodiments thereof.